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How can we know if patients in coma, vegetative state or min
Transcript of How can we know if patients in coma, vegetative state or min
Levels of Consciousness after Brain Trauma
- unconsciousness, failure to respond to stimuli (light, sound, etc.)
- absence of responsiveness and awareness. Lack of voluntary responses.
Minimally conscious state
- evidence of environmental/self-awareness, such as vocalization and knowledge of surroundings.
Consciousness is considered fluid and not necessarily stable.
Are they actually conscious?
The main purpose of this paper was to investigate the methods of measuring consciousness in post-comatose patients. Most experiments on these patients have been done with the assumption that those in a vegetative state have minimal conscious functions. The author details multiple experiments that have assumed the opposite, and talks about their contradicting conclusions.
Oddball Paradigm Experiment
Event related potentials (ERPs) are brain responses to specific stimuli. These can be used to identify signs of cognitive processing in a case of decreased consciousness. The following oddball paradigm experiment used the P300 wave to measure comatose patients's reaction to stimuli. This wave is normally sensitive to stimuli that has some significance to the patients own life, such as their own name.
In the first trial, patients listened to a conventional auditory oddball paradigm, with general noise interruptions. In the second trial, they listened to emotional verbal stimuli. P300 responses were obtained in 36-38% of comatose patients in the first trial and 52-56% of patients in the second trial. Therefore, it can be concluded that there is evidence of some conscious activity in comatose patients, especially in response to meaningful auditory stimuli.
The patient observed in the trial was a young woman who had suffered from brain trauma in a traffic accident. She was unresponsive to stimuli and did not produce spontaneous intentional behavior. She was asked to think about two things: the first, being home in her room, and the second, playing tennis. They measured her patterns of brain activity using an fMRI and compared them with those of a conscious control group. The results were indistinguishable. This is not proving that she is minimally conscious, rather than vegetative, but that there is some level of cognitive processing in the brain during such a state.
This implies that the way behavior is being assessed in states of decreased consciousness is illogical and inconclusive.
by Carson Cummins
How can we know if patients in coma, vegetative state or minimally conscious state are conscious?
Assumption: No Conscious Content
The first experiment involved comparing a vegetative patient's brain activity with healthy brain activity, as well as their own brain activity post-recovery. This experiment identified that the healthy brain activity was structured by cortico-thalamic activity. This suggests that this form of cortico-subcortical coupling is where consciousness originates.
In order to fully accept these results, it must be believed that the patient retained some ability to comprehend verbal instructions, to remember them, and to execute them. Some scientists have argued that this is simply not true. They believe that the response recorded by the fMRI was an unconscious response to the stimuli. This is due to the fact that the control group's consciousness was not the only thing creating such a signal, and the other parts of the signal-creating process were still functioning properly in the patient.
Research: A New Era
Most studies in this field are no longer focused on levels of consciousness, but on content of consciousness. Scientists aim to determine why patients are conscious of one thing and not the other. The most common research strategy, at this point, is identifying neural correlates of consciousness (NCC). For content consciousness, these are the specific minimal conditions for a certain content.
Older experiments measured consciousness through vocal response, but that is no longer applicable. A person can experience conscious content without being able to vocalize it. Therefore, the use of subjective measurements on their own is illogical. Additionally, the use of objective measurements on their own will never constitute a full picture of what it is like to be in a decreased state of consciousness.
Therefore, it was concluded that the best approach to measuring conscious content is to use both subjective and objective forms.